Musnad Ahmad 1302:22

Waki’ narrated to us, Yunus bin Abi Ishaq narrated to us, from Abu al-Safar, who said: A man from the Quraysh broke the tooth of a man from the Ansar. He sought help against him from Mu’awiyah. The Qurayshi said: "Indeed, this man has broken my tooth." Mu’awiyah said: "No, we will surely satisfy him." He said: When the Ansari persisted against him, Mu’awiyah said: "It is your affair with your companion." Abu al-Darda’ was sitting there, and Abu al-Darda’ said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'There is no Muslim who is afflicted with something in his body, and then he gives it away as charity (i.e., forgives the perpetrator), except that Allah raises him a degree by it and removes a sin from him by it.'" He said: The Ansari said: "Did you hear this from the Messenger of Allah, peace and blessings of Allah be upon him?" He said: "Yes, my ears heard it and my heart preserved it." He (the narrator) said: So he forgave him.